Abstract: The underground powerhouse of Houziyan hydropower station is located in high situ stress (mainly horizontal tectonic stress) region with complex geological conditions and big buried depth. Its first principal stress and intermediate principle stress reaches 36.43 MPa and 29.82 MPa respectively. The adverse impact couldn’t be avoided by adjusting the powerhouse axis, hence posing great challenge to the construction and support design. With this project as an example, we summarize the deformation features oflarge-span underground caverns with high intermediate stress, and discuss the deformation mechanism of surrounding rock mass according to the deformation data, support monitoring data and acoustic detection data during construction.It was found that 1)rockburst is common; 2)the deformation and failure depth are large; 3)the anchor support structure has big load level. The results of fast feedback analysis during construction period, the situ monitoring data and the acoustic detection data are used to verify the effectiveness of the support measures. We also summarized some experiences and lessons in this regard.

Key words: high intermediate principle stress, brittle rock mass, underground caverns, deformation and damage of surrounding rock, support measures